Glow plugs



F. TESTERINI Jan. 5, 1965 GLOW PLUGS Filed June 20, 1961 FIG.1

United States Patent Ofitice 3,164,748 l mented .Fan. 5, 1865 3,164,748 GLOW PLUGS Francesco Testerinhlyiilan, Italy, assignor to Fabbriea Italians Magneti Marelli i.p.A., Milan, Italy, a corporation of Italy Filed June 20, 1961, Ser. No. 113,456 Claims priority, application Italy June 28, 1960 1 Claim. (Cl. 317--98) The present invention refers to glow plugs for internal combustion engines, and of the type in which the electrical resistance is enclosed in a metal sheath, but remains separate from same by means of insulating material.

Said material is normally constituted by insulating powder which is introduced and compressed into the sheath between the electrical resistance and the sheath, and also between one spiral turn and the other in the case of spiral conductors.

In these plugs, and because of the porosity of the powor or insufficient closure of the sheath which is eifected at the extremity of this latter by means of mica or rubber silicate packing etc., during variations in the thermal conditions of the plug there occurs a flux and a reflux of air between the interior of the sheath and the outer surroundings.

In fact, when the plug heats up, the air present in the inside of the sheath due to the high temperature expands and a great part of it flows to the outside.

With the engine stopped, the plug returns to normal temperature, and the outside air together with naphtha fumes, naphtha, dust and other material are sucked back into the interior of the sheath.

In this phase, the carbon substances which are sucked in become held by the insulating material which acts as a filter, in correspondence with the inlet zone of the sheath around the electric feed supply point.

Therefore this particular zonebecomes dirty with the possibility of short circuits occurring due to the formation of layers containing carbon or other conductive material.

The short circuits are also provoked by the reduced insulating capacity of the material due to the high temperature of the zone and the high voltage present in this zone which corresponds to the total drop along the resistance from the point of connection with the electric feed intake to the nose of the sheath.

Also, on the other hand, when humidity reaches into the interior of sheath, it can be the cause of violent explosions of the armour due to the rapid creation of steam at the moment of ignition.

The object of the present invention is to obtain a plug having a perfect closure of the sheath, and at the same time incorporating major resistance strength in the zone where the electric terminal is located.

The invention is characterized by the fact that the space in which the open end of the sheath terminates is closed air tightly by means of a seal or washer in insulating material and forced by the terminal against the body and or the sheath of the glow plug.

The attached drawing which is given purely for purposes of example, illustrates an assembly arrangement of the invention.

FIGURE 1 illustrates a glow plug in partial section, and fitted with a sleeve which has still not been forced by the terminal.

FIGURE 2 illustrates the same glow plug on which however the sleeve has been forced into position.

With reference to the drawing: 1 indicates the body of the plug, 2 the sheath, and 3 the internal incandescent resistance which is connected at one end to the nose of the sheath, and at the other end to the current inductor 4 at a point which is not visible in the drawing. The insulation between the sheath and the conductor 3-4 is assured by means of a powder 5, such as magnesium oxide packed into the internal chamber of the sheath.

In correspondence with the open extremity 2 the sheath is enclosed by a resilient bush 6 of insulating material, and the lower extremity of which rests against head 7 of the body of the glow plug.

When it is not mounted this bush has a cylindrical shape with the resting base 8 having an oversize diameter.

From the side of the smaller section 9, the bush in its turn is enclosed by the hood shaped terminal 10 and which in FIGURE 1 is shown not still fitted to the bush.

The lower part 11 of the terminal is supplied with an internal conical flare 12, the smaller diameter d of which is less than the external diameter ofthe part of the bush having a reduced section 9. When the terminal is being forced into position the flare will allow the terminalto gradually wedge on part 9 of the bush, which thus becoming deformed will solidly adhere against the adjacent parts in such a manner as to air tightly close chamber 13 of the terminal in which outlets the open extremity 2 of the sheath so that the glow plug is ready for use.

FIGURE 2 shows the plug of FIG. 1 complete with the terminal and the corresponding parts are indicated by the same symbols.

The terminal is forced into bush 6 which corresponds to bush 6 of FIGURE 1, and due to the effect of radial pressure, creates the air seal between its flared part and the bush, and also between this latter part and the sheath,

whilst due to axial pressure assures air tight sealing between the bush and head 7 of the body of the plug.

in this manner chamber 13 remains hermetically sealed,

. and therefore the interior of the sheath can communicate with it, but not with the outside surroundings.

If desired the air tight seal can be made only between the bush and the terminal and the bush'and the body of the plug. In such case the internal diameter of the bush is suitably proportioned. The air seal can also be made only between the bush and the terminal, and the bush and the sheath, and in this case the bush will only rest and not be air tightly sealed on the head of the plug.

In any event and after assembly, the lower internal part of the terminal comes to act on the external surface of the part of the bush and reduced section, whilst the edge 14 of the terminal comes to act against the base 8 of the bush.

Another advantage which is obtained with the use of the bush is that there is greater strength in the connection of the terminal, inasmuch as this latter instead of working only on the current supply inductor, also works through the bush into the sheath or armour which is much more robust. As a consequence the frequent breakages in glow plugs are avoided, and which breakages occur in the critical section which corresponds in fact to the zone where the terminal is connected up.

In the case of glow plugs, where the terminal is not of the hood type, the air sealing is obtained by radial pressure by means of seals between the terminal penetrates.

I claim:

A glow plug for use in internal combustion engines,

said glow plug comprising an elongated body having an axial bore hole extending therethrough, a tubular sheath supported in the bore hole of said'elongated body and extending beyond the ends thereof, said tubular sheath being closed at one end and having an opening at the other end, an internal resistor firmly connected with the first mentioned end of said tubular sheath and extending a distance axially within said tubular sheath, a current inductor located concentrically within said sheath at the open end thereof and extending a distance beyond said sheath, said current inductor being connected with said internal resistor, an insulation powder filling said sheath, a deformable non-conductive bushing engaging one end of said elongated body and concentrically enclosing said sheath at the open end thereof, said bushing having a cylindrical portion engaging said elongated body and an inwardly tapering portion of lesser-diameter than said cylindrical portion and extending away from said elongated body, and a terminal cap enclosing said bushing and having a lower portion firmly engaging the cylindrical portion of said bushing, said terminal cap having an inner tapered portion firmly engaging and compressing the tapered portion of said bushing, said terminal cap further having an axial recess for receiving said current inductor, said terminal cap providing an air tight closure for said current inductor.

References Cited in the file of this patent UNITED STATES PATENTS 2,127,983 Nowosielski Aug. 23, 1938 2,226,849 Douglas Dec. 31, 1940 2,407,998 Richardson Sept. 24, 1946 2,672,546 Klingner et al Mar. 16, 1954 2,884,920 Moule et al. May 5, 1959 FOREIGN PATENTS 472,814 Great Britain Sept. 30, 1937 

